Construction And Application Of Lewis Acid/Base Active Center In Nanocatalysis

With the ever-increasing understanding of heterogeneous catalysis,the application of the heterogeneous catalysts has been gradually focused onthe fields of environment and energy.The heterogeneous catalysts mainly utilizeelectron-rich active center(Lewis base)or electron-deficient active center(Lewis acid)to react with active sites in the reactant with opposite charge(electron deficient or rich).Thus,the reaction barrier can be reduced and the specific reaction is promoted.The construction and application of Lewis acid and base have been widely accepted in the filed of both photocatalytic reduction of CO2 and catalysis of mediator on the counter electrode of the dye-sensitized solar cells(DSSCs),which can be realized by doping method.How to effectively construct Lewis acid/base active center by doping method,understand electron-transfer behavior,fabricate and screen high active catalysts,expand the application to the fields of environment and energy,have great scientific significance and research prospects.Therefore,in this thesis,bismuth oxybromide(BiOBr)and conductive polymer polypyrrole(PPy)that can be used as heterogeneous catalysts are used as the research subjects.The self-doping defects and anion doping methods are used respectively,constructing the Lewis acid/baseactive center and/or its multiple center so as to control the electron transfer behavior and achieve the catalysts with high performance.In BiOBr nanosheets,self-doped Bi vacancyVBi"’,namely Lewis base active center,has been successfully constructed.It is found that it can significantly enhance the chemical adsorption of CO2 and desorption of CO,promote the product selectivity,and increase the separation efficiency of photo-generated charge carriers.The calculation resultsindicate thattheBi vacancy VBi"’,on the facet {010} of BiOBr can stably exist,and reduce the activation barrier of CO2 to CO2·-.Thus,the improved photocatalytic reduction of CO2 is mainly due to the enhancement of CO2 adsorption,which may promote the activation of CO2.In BiOBr nanosheets,self-doped oxometallic defects VBi"’VO"VBi"’ and VBi"’VO",namely Lewis acid/base multiple center,have been successfully constructed.It is found that it is in favor of enhancing the visible-light absorption,separation of photo-generated charge carriers and reduction capability of electrons,while it is in disfavor of CO2 adsorption.The calculation results show that the self-doped oxometallic defects VBi1"’VO··VBi1"’ can stably exist,whereasthe VBi1"’VO·· is not that stable.The thickness of nanosheets,and the type and concentration of Bi-related vacancies together determine the photocatalytic reduction of C02.As for the counter electrode of the DSSCs,it is found that the weakly bonded I3-Playsa major role in the catalytic process.By strengthening the TsO-competitive doping and utilizing the Lewis acid of pyrrole,the PPy counter electrodes containing weakly-bonded I3-have been fabricated,which can facilitae the transfer of electrons and anions.The weakly-bonded I3-can facilitate the transfer of electrons and anions,which not only facilitate the reduction of I3-,but is also in favor of the release of I-to electrolyte,and thereby,promote the catalytic process.The catalytic process of PPy electrode on I-/I3-redox couple mainly include the following three steps:formation of weakly/strongly bondediodine species,formation of intermediates,reduction of intermediates and release of I-.The strongly-bonded doping species mainly affect the conductivity,while the weakly-bonded iodine doping species mainly influencethe catalytic activity.lt is found that the conductivity determined by the total doping amount(TsO-/I-/I3-)that can influence the exchange of anions and charges in PPy chains,the amount of surface active sites determined by the morphology and porosity,and the catalytic activity determined by the amount of the pre-stored weakly-bonded I3-(PPy···I3-),all together account for the performance of counter electrode of DSSCs.